1. Field of the Invention
The present invention relates to internal combustion engine fuel injectors in which a pump, a control valve assembly and an injector nozzle are formed in a unit, and where the pump has a follower assembly that includes a sleeve retained by a spring clip.
2. Background Art
As performance, efficiency and environmental concerns continually influence the design and operation of internal combustion engines, fuel injectors, like other components, have become more complex. Moreover, not only the structures themselves but the procedures for installing the structures may multiply the time, expense and difficultly in employing the new technological developments. This is particularly true in unit injectors in which a pump assembly, a control valve module and an injector nozzle are formed as a single unit.
In the pump assembly of the unit injector, a plunger is carried by a follower responsive to a cam, rocker arm or other reactive engine operating component relating to the combustion cycle. As the plunger is driven by the follower, the plunger chamber forms a reduced volume, high pressure fuel chamber that is coupled through a control valve assembly to the injector nozzle. The follower assembly must move freely in the direction of the plunger axis while avoiding misalignments with respect to the axis of the plunger. Moreover, while the follower is resiliently biased to an extended position for engagement with the cam, the follower must permit uniform handling, storage and installation in a mass production operation. Accordingly, reliance upon a relaxed spring state would not be sufficient to maintain uniformity of size and shape of the injector unit before installation in an engine. Moreover, while free movement of the mating surfaces permits physical contact to avoid a predetermined wear pattern in the mating surfaces, off axis movement should be constrained to avoid excessive wearing of the sliding plunger parts.
The present invention overcomes the above mentioned disadvantages by providing a fuel injector pump assembly in which a follower is formed as a sleeve that telescopically receives a portion of the injector unit body and a retainer clip is loosely retained in a groove in the sleeve and interacts with a protruding portion of the injector unit body. In general, the sleeve includes a ring groove on an inner peripheral surface of the sleeve that is wider than the cross-section of the clip stock and loosely retains the clip within the groove, permitting relative movement between the retainer ring and the sleeve. Preferably, the protruding portion of the body includes flat surfaces that are aligned with linear portions of the retainer ring. The protruding portion includes an expanded flange that restricts extraction of the ring over the end of the protrusion as the sleeve is resiliently biased toward an extended position by a spring. An end of the protruding portion has a surface opposite to the flat surface that includes a taper for displacing the clip over the end of the protruding portion during assembly.
As a result, the follower assembly allows a specified plunger stroke, while the sleeve/follower assembly maintains contact with the body to prevent side loading. Moreover, the assembly maintains a predetermined shipping height because the linear portion of the clip engages the expanded shoulder of the protruding portion. The retainer clip is easily installed by its loose capture in the groove in the sleeve, and can be snapped over the protruding body toward the linear portions of the clip, and aligning the linear clip portions with the flats on the protrusion by rotating the follower assembly while it is compressed. In the preferred embodiment, the sleeve may also include a hole over the slot between clip ends so that disassembly of the sleeve from the protruding portion of the unit injector housing can be accomplished by inserting a tool in the hole and into the gap between the ends of the clip, and rotating the follower assembly to force the linear portions of the clip outwardly as the follower assembly sleeve is rotated about the protruding portion.